# Changelog

## v0.5.0-pre

Full review implementation: HW-integration readiness, unity signal path, TX engine, spectral verification.

### Architecture changes
- All signal sources (pilot, RDS, stereo) now output unity-normalized signals (peak ±1.0)
- Combiner gains are direct config values — no magic-number normalization (`/0.1`, `/0.05` eliminated)
- Pre-emphasis moved from composite rate to audio input rate (correct signal path, efficient on SBC)
- RDS encoder: `NextSample()` zero-allocation hot path, fixed-size `[104]uint8` bit buffer
- PI validation moved to `config.Validate()` — fail-loud, no silent 0x1234 fallback

### New: TX Engine (`internal/app/engine.go`)
- Continuous chunk-based generation loop with configurable chunk duration
- Explicit `Start()`/`Stop()` — TX default is OFF
- Atomic underrun/overrun counters, chunk/sample stats
- Context-based cancellation with clean drain

### New: Extended SoapyDriver interface
- `Start(ctx)`, `Stop(ctx)`, `Capabilities(ctx)`, `Stats()` added to driver contract
- `SimulatedDriver` implements full interface with atomic runtime counters
- `DeviceCaps` struct for hardware capability reporting
- `RuntimeStats` struct for live telemetry

### New: Rate adaptation
- `backend.deviceSampleRateHz` separates SDR device rate from internal composite rate
- `Config.EffectiveDeviceRate()` resolves to device rate or falls back to composite rate

### New: Control plane upgrade
- `POST /tx/start` — explicit TX start (requires `TXController`)
- `POST /tx/stop` — explicit TX stop
- `GET /runtime` — live engine + driver telemetry
- `TXController` interface for decoupled engine control

### New: Spectral verification
- Goertzel algorithm (`dsp.GoertzelEnergy`, `dsp.BandEnergy`)
- Blackbox tests verify 19 kHz pilot, 38 kHz stereo, 57 kHz RDS energy presence
- Blackbox tests verify suppression when stereo/RDS disabled

### New: Operator truth tests
- `rds.enabled=false` → verified no 57 kHz energy
- `fmModulationEnabled=false` → verified Q=0
- `limiterEnabled=false` → verified higher peaks than with limiter
- `stereoEnabled=false` → verified no pilot/stereo energy

### Config changes
- `preEmphasisUS` → `preEmphasisTauUS` (unambiguous: microseconds, not region)
- `audio.sampleRate` → `audio.inputSampleRate` (clear: input source rate)
- `backend.deviceSampleRateHz` added (0 = same as compositeRateHz)
- `rds.pi` validated at load time; empty/invalid = hard error
- `rds.pty` range-checked (0-31)

## v0.4.0-pre
[previous changelog entries]